In an Otto-engine combustion method, which is frequently referred to in the literature as a gasoline HCCI method (homogeneous charge compression ignition) or as a CAI method (controlled auto ignition), a fuel injected into an internal combustion engine is combusted without external ignition. The fuel is instead automatically ignited by mixture of the injected fuel with a hot exhaust gas and subsequent compression of the fuel-gas mixture.
CAI engines are typically equipped with a variable valve drive and a gasoline direct injection. One differentiates between a fully-variable valve drive, implemented by an electrohydraulic valve controller, for example, and a partially-variable valve drive, e.g., a valve drive controlled using the camshaft having two-point stroke and phase adjuster. The latter represents the more cost-effective alternative.
Because the hot residual gas in the internal combustion engine is responsible for initiating the combustion during the compression phase in a CAI operation, it is desirable to have a relatively large quantity of residual gas before the combustion in the cylinder. For example, an internal exhaust gas quantity may be kept in the cylinder because of negative valve overlaps. Additionally or alternatively thereto, an external exhaust gas quantity may be returned or sucked back in by briefly opening the outlet valve during the intake phase.
In addition to the exhaust gas quantity, the exhaust gas temperature is also significant for the ignition of the fuel injected into the internal combustion engine. Because the exhaust gas temperature is a function of the point in time of the preceding combustion, there is a relationship between a combustion point of a first cycle and the combustion point of the following second cycle. For example, an excessively late ignition of the fuel in the first cycle may trigger a premature ignition during the second cycle. A premature ignition during the first cycle correspondingly frequently causes a delay or a miss in the ignition of the fuel during the second cycle.
It is therefore desirable to have a possibility for preventing irregularities in the ignition of a fuel injected into a compression-ignition internal combustion engine.